I have a friend that has an unmolested 74 Duster with a 318 & OEM floor shift 3 speed trans. The engine is being rebuilt with a small cam and the addition of a 4 bbl manifold and carb. He would like to change to a 4 speed (non overdrive A833). I understand that the 318 bellhousing is drilled for both the 3 & 4 spd transmissions and am looking for information on this conversion. Does the cross member and/or driveshaft need to be replaced or modified? Also possible sources for a serviceable trans and any other information pertaining to such a swap would be appreciated.